Braided stent with expansion ring and method of delivery

ABSTRACT

A self-expanding braided stent includes at least a distal radial expansion ring added to a distal end of the stent body to increase a radial expansion force of the self-expanding braided stent in deployment of the stent, and to facilitate advancement of the stent through a delivery sheath by a core advancement wire. A proximal radial expansion ring is optionally added to a proximal end of the stent body to allow the stent to be recaptured following partial deployment by retraction of the core advancement wire, prior to full deployment of a proximal portion of the stent body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Pat. ApplicationNo. 15/980,961 filed May 16, 2018, which is a divisional application ofU.S. Pat. Application No. 13/802,114 filed Mar. 13, 2013, now issued asU.S. Pat. No. 10,561,509 on Feb. 18, 2020, the contents of all of whichare incorporated herein by reference in their entirety as if set forthverbatim.

BACKGROUND OF THE INVENTION

This invention relates generally to devices for interventionaltherapeutic treatment or vascular surgery for treatment of defects inthe vasculature, and more particularly concerns a system and method fordelivering a self-expanding braided stent to a treatment site in avasculature of a patient.

Stents, which are tubular reinforcements inserted into a blood vessel toprovide an open path within the blood vessel, have been widely used inintravascular angioplasty treatment of occluded cardiac arteries. Insuch applications, the stent is inserted after an angioplasty procedureor the like in order to prevent restenosis of the artery. In theseapplications, the stents are often deployed by use of inflatableballoons, or mechanical devices which force the stent open, therebyreinforcing the artery wall and provide a clear through-path in thecenter of the artery after the angioplasty procedure to preventrestenosis.

While such procedures may be useful in certain aspects of vascularsurgery in which vasoocclusive devices are used, the weakness andtortuosity of the neurovasculature places limits on the applicability ofsuch stents in procedures to repair neurovascular defects. Furthermore,the use of placement techniques, such as balloons or mechanicalexpansions of the type often found to be useful in cardiac surgery, arerelatively less useful in vasoocclusive surgery, particularly when tinyvessels, such as those found in the brain, are to be treated. Hence,those skilled in the art have recognized a need for a stent compatiblewith techniques in vasoocclusive treatment of neurovascular defects thatprovides selective reinforcement in the vicinity of a neurovasculardefect, while avoiding any unnecessary trauma or risk of rupture to theblood vessel.

Braided stents, typically formed from a plurality of elongate members,such as two or more metal wires, or polymeric fibers or strands ofmaterial, for example, can be very useful in treatment of neurovasculardefects. However, one of the problems in deploying a self-expandingbraided stent in a body lumen is activation of the initially expandingend, typically the distal end of the braided stent, to fully open. It isimportant that the initially expanding end should open fully, easily,and quickly, so that the rest of the length of self-expanding braidedstent can be deployed, using the initially expanding end as an anchorpoint.

Stents made of braided wire also commonly have a high internal frictionthat resists the inherent radial expansion force of the self-expandingbraided stent to open, particularly resisting opening of the initiallyexpanding end, which can cause problems in anchoring and deployment ofsuch self-expanding braided stents. Another common problem withdeployment of braided stents is difficulty in advancing the compressedor crimped braided stent through a delivery sheath or microcatheter,typically also due to friction between the braided stent and thedelivery sheath or microcatheter. Traditional delivery systems forbraided stents push the braided stent in a distal direction by advancinga blunt surface against a proximal end of the braided stent, andconsequently the application of force on the proximal end of the braidedstent tends to axially compress the braided stent, causing the braidedstent to expand radially. As a result, as the braided stent expandswithin the delivery sheath or microcatheter, an increased normal forceis applied to the inner surface of the delivery sheath or microcatheter,increasing friction between the braided stent and the delivery sheath ormicrocatheter.

Current self-expanding braided stents typically depend solely on theirmaterial, dimension, cell design, and internal friction to expand.Deployment of such self-expanding braided stents commonly requires extramanipulation by a user to fully open the self-expanding braided stents,which affects placement accuracy and adds risk to the procedure. Properdeployment and fixation of the initial deployment end or distal end of aself-expanding braided stent are necessary for the subsequent properalignment and positioning of the remainder of the stent body.

Another problem with deployment of self-expanding braided stentsinvolves difficulty in recapturing a self-expanding braided stent afterpartial deployment and prior to full deployment of the stent. Currently,a self-expanding braided stent typically is advanced through a deliverysheath or microcatheter until the self-expanding braided stent emerges.When the self-expanding braided stent is unrestrained outside of thesheath or microcatheter, the self-expanding braided stent typically thenexpands and is deployed in the vasculature, making recapturing of theself-expanding braided stent difficult. self-expanding braided stentwith increased radial expansion force, particularly at the initialdeployment end or distal end, that can also reduce the internal frictionof the braided stent during delivery of the braided stent through adelivery sheath or microcatheter, for improved ease and reliability ofdeployment of the self-expanding braided stent, particularly at theinitial deployment end or distal end of the self-expanding braidedstent.

It also would be desirable to provide an improved self-expanding braidedstent that can be recaptured following partial deployment of a distalportion of the self-expanding braided stent prior to full deployment ofa later deployed portion or proximal portion of the self-expandingbraided stent. The present invention meets these and other needs.

SUMMARY OF THE INVENTION

Briefly and in general terms, the present invention provides for animproved self-expanding braided stent with one or more expansion rings,and methods of delivering the self-expanding braided stent through adelivery sheath or microcatheter to a treatment site in a patient’svasculature. The present invention provides for the addition of at leastone radial expansion ring to an initial deployment end or distal end ofa self-expanding braided stent to increase a radial expansion force ofthe self-expanding braided stent, for improved ease and reliability ofdeployment of the self-expanding braided stent, and particularly morereliable expansion and fixing of the initial deployment end or distalend of the self-expanding braided stent in deployment of theself-expanding braided stent. The addition of a radial expansion ring toa later deployed end or proximal end of a self-expanding braided stentallows the self-expanding braided stent to be recaptured followingpartial deployment of a distal portion of the self-expanding braidedstent, and prior to full deployment of a later deployed portion orproximal portion of the self-expanding braided stent.

Accordingly, in a first embodiment, the present invention provides for abraided stent, including a tubular braided stent body formed from aplurality of elongate members, and one or more expansion rings disposedwithin and fixedly connected to at least one of the proximal end and thedistal end of the tubular braided stent body. In a presently preferredaspect, the one or more expansion rings have a compressed configurationhaving a first diameter and an expanded configuration having a seconddiameter larger than the first diameter. In another presently preferredaspect, the plurality of elongate members may be formed by a pluralityof metal wires, a plurality of polymeric fibers, a plurality of strandsof material, or the like. In another presently preferred aspect, thebraided stent is a self-expanding stent having a compressedconfiguration having an unexpanded diameter and an expandedconfiguration having an expanded diameter larger than the firstdiameter.

In another presently preferred aspect, the one or more expansion ringsinclude a plurality of elongated connecting arm members having firstends at the first end of the one or more expansion rings and second endsat the second end of the expansion ring, and the plurality of elongatedconnecting arm members are connected sequentially to adjacent ones ofthe plurality of elongated connecting arm members alternatingly at thefirst and second ends to form a plurality of alternating elbowconnections at the first and second ends, such as in a zigzagconfiguration, for example. In another presently preferred aspect, theone or more expansion rings are formed of shape memory material, such asa nickel titanium alloy or a shape memory polymer, for example, having ashape memory position in the expanded configuration. Preferably the oneor more expansion rings is heat treated so that the shape memoryposition is an expanded zigzag type ring, and the plurality of elongatedconnecting arm members and the alternating elbow connections preferablyare configured to be compressed into a small tubular shape duringdelivery. In another presently preferred aspect, the one or moreexpansion rings include a plurality of attachment tabs connected to theplurality of alternating elbow connections at the first ends of the oneor more expansion rings, and preferably the plurality of alternatingelbow connections at the first ends of the one or more expansion ringshave exterior ends directed away from the plurality of elongatedconnecting arm members, and the plurality of attachment tabs areconnected to the exterior ends of the plurality of alternating elbowconnections at the first ends of the one or more expansion rings. Theplurality of attachment tabs preferably are fixedly attached to thetubular braided stent body, such as by welding, soldering or gluing theattachment tabs to an expansion ring, for example. Alternatively, theattachment tabs can include holes in them so that a wire loop can bethreaded through the attachment tabs, as well as through interstices ofthe braided stent to connect the attachment tabs and the braided stenttogether. In addition, two or more attachment tabs can be included atthe ends of each elbow of the expansion ring, and the attachment tabscan then be used to capture a portion of the braided stent between them,after which the two or more attachment tabs can be secured together tobe permanently secured to the braided stent by welding, soldering,adhesive, or the like. In another presently preferred aspect, anexpansion ring is disposed within and fixedly connected to the initialdeployment end or distal end of the tubular braided stent body, and aproximal expansion ring optionally also may be disposed within andfixedly connected to the later deployed end or proximal end of thetubular braided stent body.

In another presently preferred aspect, a core advancement wire isprovided that is disposed within and extends through the lumen of thetubular braided stent body and the lumen of a distal expansion ring, andwhen a proximal expansion ring is provided, the core advancement wireextends through the lumen of the proximal expansion ring as well, fordelivering and releasing the self-expanding stent through a deliverysheath or microcatheter to a treatment site in a patient’s vasculature.The core advancement wire preferably includes a proximal portion, adistal portion, an intermediate portion located between the proximal anddistal portions of the core advancement wire, and a stop memberpositioned between the distal portion and the intermediate portion ofthe core advancement wire. In a presently preferred aspect, the stopmember is formed by an enlarged portion of the core advancement wirehaving a diameter greater than or equal to the first diameter of thecompressed configuration of the expansion ring. In another presentlypreferred aspect, the stop member is configured to engage a proximal,interior side of the distal expansion ring when the core advancementwire is advanced distally, whereby force applied distally to the coreadvancement wire is transmitted through the distal expansion ring to theinitial deployment end or distal end of the braided stent and acts todrag and elongate the braided stent distally. The braided stent istypically configured to be delivered through the delivery sheath ormicrocatheter, and the core advancement wire is preferably configured toreduce friction of the braided stent with the delivery sheath ormicrocatheter when force is applied distally to the core advancementwire.

In another presently preferred aspect, when a proximal expansion ring isprovided, the core advancement wire includes an intermediate stop memberon the core advancement wire positioned on the intermediate portion ofthe core advancement wire within the lumen of the braided stent distalto the second expansion ring. In a presently preferred aspect, theintermediate stop member includes an enlarged portion of the coreadvancement wire having a diameter greater than or equal to the firstdiameter of the compressed configuration of the second expansion ring.

In another presently preferred aspect, the present invention providesfor a method of delivering and releasing the self-expanding stentthrough a delivery sheath or microcatheter to a treatment site in apatient’s vasculature, including the step of advancing the coreadvancement wire distally such that the distal stop member engages aproximal, interior side of the distal expansion ring, whereby forceapplied distally to the core advancement wire is transmitted through thedistal expansion ring to the initial deployment end or distal end of thetubular self-expanding braided stent acting to drag and elongate thetubular self-expanding braided stent, reducing friction of the tubularself-expanding braided stent with the delivery sheath or microcatheterwhen force is applied distally to the core advancement wire. In anotherpresently preferred aspect, the method includes the steps of draggingthe distal expansion ring of the tubular self-expanding braided stentdistally of the delivery sheath or microcatheter while retaining theproximal expansion ring of the tubular self-expanding braided stentwithin the delivery sheath or microcatheter, retracting the coreadvancement wire proximally such that the intermediate stop memberengages a distal, interior side of the proximal expansion ring,retracting the initial deployment end or distal end of the tubularself-expanding braided stent within the delivery sheath or microcathetersuch that the distal expansion ring and the initial deployment end ordistal end of the tubular self-expanding braided stent are reduced indiameter, and recapturing the tubular self-expanding braided stentwithin the delivery sheath or microcatheter.

These and other features and advantages of the present invention willbecome more apparent from the following detailed description of thepreferred embodiments in conjunction with the accompanying drawings,which illustrate, by way of example, the operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an expansion ring configured to beaffixed within a braided stent, according to the invention.

FIG. 2 is a cross-sectional schematic elevational view of an expansionring of FIG. 1 affixed within an initial deployment end or distal end ofa braided stent, shown contained within a delivery sheath ormicrocatheter, according to the invention.

FIG. 3 is a cross-sectional schematic elevational view similar to FIG. 2, showing partial deployment of the initial deployment end or distal endof the braided stent from the delivery sheath or microcatheter of FIG. 2.

FIG. 4 is a cross-sectional schematic elevational view of an expansionring of FIG. 1 affixed within an initial deployment end or distal end ofa braided stent, shown contained within a delivery sheath ormicrocatheter, and including a core advancement wire extending throughthe braided stent and expansion ring, according to the invention.

FIG. 5 is a cross-sectional schematic elevational view similar to FIG. 4, showing partial deployment of the initial deployment end or distal endof the braided stent from the delivery sheath or microcatheter of FIG. 4.

FIG. 6 is a cross-sectional schematic elevational view of a braidedstent having a distal expansion ring and a proximal expansion ringaffixed within the distal and proximal ends of the braided stent, showncontained within a delivery sheath or microcatheter, and including acore advancement wire extending through the braided stent and expansionring, according to the invention.

FIG. 7 is a cross-sectional schematic elevational view similar to FIG. 6, showing partial deployment of the initial deployment end or distal endof the braided stent from the delivery sheath or microcatheter of FIG. 6.

FIG. 8 is a cross-sectional schematic elevational view similar to FIG. 6, showing retraction of the initial deployment end or distal end of thebraided stent into the delivery sheath or microcatheter of FIG. 6 .

FIG. 9 is a cross-sectional schematic elevational view similar to FIG. 6, showing implantation of a braided stent at a treatment site in apatient’s vasculature, and withdrawing of the core advancement wire anddelivery sheath or microcatheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While stents have commonly been delivered in in blood vessels such asduring intravascular angioplasty treatment of occluded cardiac arteries,by use of inflatable balloons or mechanical devices that force a stentopen, the weakness and tortuosity of the neurovasculature places limitson the applicability of such stents in procedures to repairneurovascular defects, and it is desirable to provide an improvedself-expanding braided stent with increased its radial expansion force,particularly at the initial deployment end or distal end, that can alsoreduce the internal friction of the braided stent during delivery of thebraided stent through a delivery sheath or microcatheter, that can bemore reliably expanded and fixed at the initial deployment end or distalend of the self-expanding braided stent, and that can be recapturedfollowing partial deployment of a distal portion of the self-expandingbraided stent prior to full deployment of a later deployed portion orproximal portion of the self-expanding braided stent.

Accordingly, referring to the drawings, which are provided by way ofexample, and not by way of limitation, in a first embodiment, fortreatment of a patient’s vasculature, the present invention provides fora braided stent 10 including a tubular braided stent body 11, having alater deployed end or proximal end 12, an initial deployment end ordistal end 14, and an inner lumen 16 as shown in FIG. 1 . The tubularbraided stent body is preferably formed from a plurality of elongatemembers 18, typically formed from two or more metal wires, or polymericfibers or strands of material, for example. In a presently preferredaspect, the braided stent is a self-expanding stent, and includes one ormore expansion rings 20, each having a first end 22, a second end 24,and an inner lumen 26. The one or more expansion rings preferably aredisposed within and fixedly connected to at least the initial deploymentend or distal end of the tubular braided stent body, although one ormore expansion rings may also be disposed within and fixedly connectedto the later deployed end or proximal end of the tubular braided stentbody, as will be further explained below.

Each expansion ring includes a plurality of elongated connecting armmembers 30 having first ends 32 at the first end of the expansion ring,and second ends 34 at the second end of the expansion ring. Theplurality of elongated connecting arm members 30 are connectedsequentially to adjacent ones of the plurality of elongated connectingarm members 30 alternatingly at the first and second ends (32, 34) toform a plurality of alternating elbow connections 36 at the first andsecond ends of the expansion ring 20, so that the plurality of elongatedconnecting arm members 30 of each expansion ring 20 substantially have azigzag configuration.

Referring to FIGS. 2, 3 and 4 , each expansion ring preferably is formedto have a compressed configuration 38, having a first diameter, and anexpanded configuration 42, having a second diameter that is larger thanthe first diameter of the compressed configuration 38 of the expansionring 20. Each expansion ring 20 is preferably formed of a shape memorymaterial such as a nickel-titanium alloy, or a shape memory polymer, forexample, having a shape memory position in the expanded configuration42. For example, the expansion rings 20 may be appropriately heattreated so that the expansion ring 20 forms in the desired shape of theexpanded shape memory position 42, with the plurality of elongatedconnecting arm members 30 having a substantially zigzag typeconfiguration. Each expansion ring 20 is typically formed by cutting atube formed of a shape memory material such as a nickel-titanium alloy,or a shape memory polymer, for example, by an appropriate laser. Theplurality of elongated connecting arm members 30 and the alternatingelbow connections 36 preferably can be compressed in the compressedconfiguration 38 into a tubular shape that is small enough tocomfortably fit within and pass through a delivery sheath ormicrocatheter 44 to allow delivery of the stent through the deliverysheath or microcatheter 44 to a treatment site in a patient’svasculature 52.

In another presently preferred aspect, each expansion ring 20 includes aplurality of attachment tabs 46 connected to the plurality ofalternating elbow connections 36 at the first ends 32 of the expansionring 20. The plurality of attachment tabs 46 preferably are connected toexterior ends 48 of the plurality of alternating elbow connections 36 atthe first ends 32 of the one or more expansion ring 20. The plurality ofattachment tabs 46 preferably are fixedly connected to a tubular braidedstent body 10, typically at or near a distal 14 or proximal 12 end ofthe tubular braided stent body 10, such as by welding, soldering, orgluing by an appropriate adhesive, for example. Alternatively, theattachment tabs 46 can include holes in them so that a wire loop can bethreaded through the attachment tabs 46, as well as through intersticesof the braided stent 10 to connect the attachment tabs 46 and thebraided stent 10 together. In addition, two or more attachment tabs 46can be included at the ends of each elbow connection 36 of the expansionring 20, and the attachment tabs 46 can then be used to capture aportion of the braided stent 10 between them, after which the two ormore attachment tabs 46 can be secured together to be permanentlysecured to the braided stent 10 by welding, soldering, adhesive, or thelike. At least one first, distal, expansion ring 20 a preferably isdisposed within and fixedly connected to the initial deployment end ordistal end 14 of the tubular braided stent body 10. As is illustrated inFIGS. 6-9 , a second, proximal, expansion ring 20 b preferably also isdisposed within and fixedly connected to the later deployed end orproximal end 14 of the tubular braided stent body 10.

Referring to FIGS. 4-9 , in a second embodiment, in which like elementsare indicated by like reference numbers, the present invention furtherprovides for an apparatus 50 for delivering and releasing aself-expanding braided stent 10 through a delivery sheath ormicrocatheter 44 to a treatment site in a patient’s vasculature 52. Theapparatus includes a braided stent including a tubular braided stentbody 10, described above, and also includes a core advancement wire 54,which is disposed within and extends through the lumen of the tubularbraided stent body 10, and is disposed within and extending through thelumen of the distal expansion ring 20 a fixedly connected within theinitial deployment end or distal end 12 of the tubular braided stentbody 10. When a proximal expansion ring 20 b is fixedly connected withinthe later deployed end or proximal end 12 of the tubular braided stentbody 10, as is illustrated in FIGS. 6-9 , the core advancement wire 54also is disposed within and extends through the lumen of the proximalexpansion ring 20 b.

The core advancement wire 54 includes a proximal portion 56, a distalportion 58, an intermediate portion 60 located between the proximal anddistal portions of the core advancement wire 54, and a distal stopmember 62 positioned between the distal portion 58 and the intermediateportion 60 of the core advancement wire 54. In one presently preferredaspect, as is shown in FIG. 4 , the distal stop member 62 is formed asan enlarged portion of the core advancement wire 54 having a diametergreater than or equal to the first diameter of the compressedconfiguration 38 of the expansion ring 20. The distal stop member 62 ispreferably configured to engage a proximal, interior side 64 of thedistal expansion ring 20 a when the core advancement wire 54 is advanceddistally, so that force applied distally to the core advancement wire 54is transmitted through the distal stop member 62 to the distal expansionring 20 a, and consequently is transmitted to the initial deployment endor distal end 14 of the braided stent 10, thereby acting to drag thebraided stent 10 in a distal direction, as the braided stent 10 isdelivered through the delivery sheath or microcatheter 44 to a treatmentsite, as well as to elongate the braided stent 10 , advantageously alsoreducing friction with the delivery sheath or microcatheter 44 throughwhich the braided stent 10 is delivered.

In another preferred aspect, a proximal stop member 66 may also beprovided on the core advancement wire 54 positioned outside and proximalto the proximal end 12 of the braided stent 10. When it is provided, theproximal stop member 66 preferably has a diameter greater than or equalto the unexpanded diameter of the compressed configuration 38 of thebraided stent 10 and less than a diameter of the delivery sheath ormicrocatheter 44.

The self-expanding braided stent 10 can be delivered and releasedthrough the delivery sheath or microcatheter 44 to a treatment site in apatient’s vasculature by advancing the core advancement wire 54 distally(to the left as shown), so that the distal stop member 62 of the coreadvancement wire 54 engages the proximal, interior side 64 of the distalexpansion ring 20 a. Since the distal expansion ring 20 a is attached tothe braided stent 10, force applied distally to the core advancementwire 54 is transmitted through the distal expansion ring 20 a to theinitial deployment end or distal end 14 of the braided stent 10, and theforce applied to the initial deployment end or distal end 14 of thebraided stent 10 in the distal direction therefore tends to drag andelongate the braided stent 10, consequently reducing the diameter of thecompressed configuration 38 of the braided stent 10, reducing thefriction between the braided stent 10 and the delivery sheath ormicrocatheter 44.

In another embodiment illustrated in FIGS. 6-9 , in which like elementsare indicated by like reference numbers, the present invention furtherprovides for an apparatus for delivering and releasing a self-expandingbraided stent 10 through a delivery sheath or microcatheter 44 to atreatment site in a patient’s vasculature, in which the core advancementwire 54 also includes an intermediate stop member 68 positioned on theintermediate portion 60 of the core advancement wire 54, within thelumen of the braided stent 10 distal to the proximal expansion ring 20b. The intermediate stop member 68 preferably is formed as an enlargedportion of the core advancement wire 54 having a diameter that isgreater than or equal to the first diameter of the compressedconfiguration 38 of the proximal expansion ring 20 b. The intermediatestop member 68 preferably is configured to engage the distal, interiorside 70 of the proximal expansion ring 20 b when the core advancementwire 54 is retracted proximally, allowing retraction of the braidedstent 10 within the delivery sheath or microcatheter 44.

In this embodiment, the self-expanding braided stent 10 can be deliveredand released through the delivery sheath or microcatheter 44 to atreatment site in a patient’s vasculature by advancing the coreadvancement wire 54 distally, as described above, and the coreadvancement wire 54 may also then be retracted proximally (to the rightas shown in FIG. 8 ), so that the intermediate stop member 68 engagesthe distal, interior side 70 of the proximal expansion ring 20 b. Aslong as the braided stent 10 is not deployed past the proximal expansionring 20 b, the braided stent 10 can be recaptured in this way. Theretraction force applied proximally to the core advancement wire 54 istransmitted through the proximal expansion ring 20 b to the proximal end12 of the braided stent 10, and as the braided stent 10 is recapturedback into the delivery sheath or microcatheter 44, the initialdeployment end or distal end 14 of the braided stent 10 is reduced indiameter by the mouth 72 of the delivery sheath or microcatheter 44until the braided stent 10 is again fully enclosed by the deliverysheath or microcatheter 44.

It will be apparent from the foregoing that while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

We claim:
 1. An apparatus for delivering and releasing a self-expandingbraided stent through a delivery sheath to a treatment site in apatient’s vasculature, said apparatus comprising: a tubularself-expanding braided stent body having a proximal end, a distal end,and an inner lumen, said tubular self-expanding braided stent body beingformed from a plurality of elongate members, said tubular self-expandingbraided stent body having a compressed configuration and an expandedconfiguration; at least one expansion ring disposed within and fixedlyconnected to said distal end of said tubular self-expanding braidedstent body, said at least one expansion ring having a proximal interiorend, a distal exterior end approximate the distal end of said tubularself-expanding braided stent body, and an inner lumen, said at least oneexpansion ring having a compressed configuration having a first diameterand an expanded configuration having a second diameter larger than saidfirst diameter; a core advancement wire disposed within and extendingthrough said inner lumen of said tubular self-expanding braided stentbody and said inner lumen of said at least one expansion ring, said coreadvancement wire having: a proximal portion, a distal portion, anintermediate portion located between said proximal and distal portionsof said core advancement wire, a proximal stop member on said coreadvancement wire positioned outside and proximal to said proximal end ofsaid tubular self-expanding braided stent body, said proximal stopmember having a diameter greater than or equal to an unexpanded diameterof the compressed configuration of said tubular self-expanding braidedbody and less than a diameter of the delivery sheath, and a distal stopmember positioned between said distal portion and said intermediateportion of said core advancement wire and immediately adjacent to saidproximal interior end of said at least one expansion ring, said distalstop member being configured to press distally into said proximalinterior end of said at least one expansion ring when the said coreadvancement wire is advanced distally, whereby force applied distally tosaid core advancement wire is transmitted through said at least oneexpansion ring to said distal end of said tubular self-expanding braidedstent body and acts to drag and elongate said tubular self-expandingbraided stent body, and wherein said core advancement wire is configuredto reduce friction of said tubular self-expanding braided stent bodywith said delivery sheath when force is applied distally to said coreadvancement wire.
 2. The apparatus of claim 1, wherein said at least oneexpansion ring is formed of shape memory material having a shape memoryposition in said expanded configuration.
 3. The apparatus of claim 1,wherein said at least one expansion ring comprises a plurality ofelongated connecting arm members having first ends at said first end ofsaid at least one expansion ring and second ends at said second end ofsaid at least one expansion ring, said plurality of elongated connectingarm members being connected sequentially to adjacent ones of saidplurality of elongated connecting arm members alternatingly at saidfirst and second ends to form a plurality of alternating elbowconnections at said first and second ends.
 4. The apparatus of claim 3,further comprising a plurality of attachment tabs connected to saidplurality of alternating elbow connections at said proximal interior endof said at least one expansion ring, wherein said plurality ofalternating elbow connections at said proximal interior end of said atleast one expansion ring have exterior ends directed away from saidplurality of elongated connecting arm members and said plurality ofattachment tabs are connected to said exterior ends of said plurality ofalternating elbow connections at said proximal interior end of said atleast one expansion ring, and wherein said plurality of attachment tabsare fixedly attached to said tubular self-expanding braided stent body.5. The apparatus of claim 1, wherein said distal stop member comprisesan enlarged portion of said core advancement wire having a diametergreater than or equal to said first diameter of said compressedconfiguration of said at least one expansion ring disposed within andfixedly connected to said distal end of said tubular self-expandingbraided stent body.
 6. The apparatus of claim 1, further comprising asecond expansion ring having a distal interior end, a proximal exteriorend, and an inner lumen, the second expansion ring being disposed withinand fixedly connected to said proximal end of said tubularself-expanding braided stent body, said core advancement wire furtherincluding an intermediate stop member on said core advancement wirepositioned on said intermediate portion of said core advancement wirewithin said inner lumen of said tubular self-expanding braided stentbody.
 7. The apparatus of claim 6, wherein said intermediate stop memberis positioned within said inner lumen of said tubular self-expandingbraided stent body distal to said second expansion ring and immediatelyadjacent to said distal interior end of said second expansion ring. 8.The apparatus of claim 7, wherein said intermediate stop membercomprises an enlarged portion of said core advancement wire having adiameter greater than or equal to a first diameter of a compressedconfiguration of said second expansion ring.
 9. An apparatus fordelivering and releasing a self-expanding stent through a deliverysheath to a treatment site in a patient’s vasculature, said apparatuscomprising: a tubular self-expanding braided stent body having aproximal end, a distal end, and an inner lumen, said tubularself-expanding braided stent body being formed from a plurality ofelongate members, said tubular self-expanding braided stent body havinga compressed configuration and an expanded configuration; a distalexpansion ring and a proximal expansion ring, said distal expansion ringdisposed within and fixedly connected to said distal end of said tubularself-expanding braided stent body, said proximal expansion ring disposedwithin and fixedly connected to said proximal end of said tubularself-expanding braided stent body, said distal expansion ring having aproximal interior end, a distal exterior end approximate the distal endof said tubular self-expanding braided stent body, and an inner lumen,and said proximal expansion ring having a distal interior endapproximate the proximal end of said tubular self-expanding braidedstent body, a proximal exterior end, and an inner lumen, each of saiddistal and proximal expansion rings having a compressed configurationhaving a first diameter and an expanded configuration having a seconddiameter larger than said first diameter; and a core advancement wiredisposed within and extending through said inner lumen of said tubularself-expanding braided stent body and said inner lumen of said distaland proximal expansion rings, said core advancement wire having: aproximal portion, a distal portion, an intermediate portion locatedbetween said proximal and distal portions of said core advancement wire,a distal stop member positioned between said distal portion and saidintermediate portion of said core advancement wire within said innerlumen of said tubular self-expanding braided stent body distal to saidproximal expansion ring and immediately adjacent to said proximalinterior end of said distal expansion ring, said distal stop memberbeing configured to press distally into said proximal interior end ofsaid distal expansion ring when the said core advancement wire isadvanced distally, whereby force applied distally to said coreadvancement wire is transmitted through said distal expansion ring tosaid distal end of said tubular self-expanding braided stent body andacts to drag and elongate said tubular self-expanding braided stentbody, and an intermediate stop member positioned on said intermediateportion of said core advancement wire within said inner lumen of saidtubular self-expanding braided stent body distal to said proximalexpansion ring and immediately adjacent to said distal interior end ofsaid proximal expansion ring, said intermediate stop member beingconfigured to press proximally into said distal interior end of saidproximal expansion ring when said core advancement wire is retractedproximally, allowing retraction of said tubular self-expanding braidedstent body within the delivery sheath, wherein said core advancementwire is configured to reduce friction of said tubular self-expandingbraided stent body with said delivery sheath when force is applieddistally to said core advancement wire.
 10. The apparatus of claim 9,wherein at least one of said proximal expansion ring and said distalexpansion ring is formed of shape memory material having a shape memoryposition in said expanded configuration.
 11. The apparatus of claim 9,wherein each of said distal and proximal expansion rings include aplurality of elongated connecting arm members having first ends at saidproximal interior end of said distal expansion ring and said distalinterior end of said proximal expansion ring and second ends at saiddistal exterior end of said distal ring and said proximal exterior endof said proximal expansion ring, said plurality of elongated connectingarm members being connected sequentially to adjacent ones of saidplurality of elongated connecting arm members alternatingly at saidfirst and second ends to form a plurality of alternating elbowconnections at said first and second ends having a zigzag configuration,and wherein said plurality of elongated connecting arm members and saidplurality of alternating elbow connections are configured to becompressed into a small tubular shape during delivery.
 12. The apparatusof claim 11, further comprising a plurality of attachment tabs connectedto said plurality of alternating elbow connections at said proximalinterior end of said distal expansion ring and said distal interior endof said proximal expansion ring, wherein said plurality of alternatingelbow connections at said proximal interior end of said distal expansionring and said distal interior end of said proximal expansion ring haveexterior ends directed away from said plurality of elongated connectingarm members and said plurality of attachment tabs are connected to saidexterior ends of said plurality of alternating elbow connections at saidproximal interior end of said distal expansion ring and said distalinterior end of said proximal expansion ring, and wherein said pluralityof attachment tabs are fixedly attached to said tubular self-expandingbraided stent body.
 13. The apparatus of claim 9, wherein said distalstop member comprises an enlarged portion of said core advancement wirehaving a diameter greater than or equal to said first diameter of saidcompressed configuration of said distal expansion ring.
 14. Theapparatus of claim 9, further comprising a proximal stop member on saidcore advancement wire positioned outside and proximal to said proximalend of said tubular self-expanding braided stent body, said proximalstop member having a diameter greater than or equal to said firstdiameter of said compressed configuration of said distal expansion ringand less than a diameter of the delivery sheath.
 15. The apparatus ofclaim 9, wherein said intermediate stop member comprises an enlargedportion of said core advancement wire having a diameter greater than orequal to said first diameter of said compressed configuration of saidproximal expansion ring.